One of the applications of the jam tolerant electromechanical actuation systems of this invention, among others, is for the actuation of thin wing stabilizers (both vertical and horizontal), ailerons, canards, rudders for manned and unmanned aircraft, marine, submarine, spacecraft, as well as ground vehicles and the like. This invention makes electromechanical actuators safer for primary flight control since it eliminates a mechanical jam potential in electromechanical actuators and thereby removes the last remaining technical obstacle that prevents electromechanical actuators from being used in primary flight control applications.
The patent literature includes a number of constructions that pertain to jam tolerant hinge line actuators, or other electromechanical actuators, that utilize frangible elements or other mechanisms to relieve a jam when an overload occurs. The patents listed below are merely representative of the prior art and are listed in chronological order as follows: U.S. Pat. No. 3,958,779 to Townsend; U.S. Pat. No. 4,544,052 to Borden; U.S. Pat. No. 4,637,272 to Teske et al.; U.S. Pat. No. 4,885,939 to Martin; U.S. Pat. No. 4,932,613 to Tiedeman et al.; U.S. Pat. No. 4,979,700 to Tiedeman et al.; U.S. Pat. No. 5,071,397 to Grimm; U.S. Pat. No. 5,518,466 to Tiedeman; U.S. Pat. No. 5,779,587 to Reilly; U.S. Pat. No. 5,947,246 to Koller; U.S. Pat. No. 6,231,012 B1 to Cacciola et al.; U.S. Pat. No. 6,260,799 B1 to Russ; U.S. Pat. No. 6,443,034 B1 to Capewell et al.; and U.S. Pat. No. 6,705,570 to Degenholtz et al. Several of these constructions will be discussed in more detail as follows:
Turning first to U.S. Pat. No. 3,958,779 to Townsed, pertains to jam tolerant surface control but not to a hinge line actuator. U.S. Pat. No. 4,932,613 to Tiedeman et al. incorporates a two slice hinge planetary mechanism which uses helical gearing to provide greater torque output for a given volume. The helix angles are opposite between left and right slices such that the thrust loads generated on these gears will act towards each other and ultimately cancel each other out. Thus there does not need to be any additional structure to carry the thrust loads. The structures of the present invention do not utilized opposing helical gears. U.S. Pat. No. 5,518,466 to Tiedeman achieves jam tolerance through the use of frangible elements at both the input and output of the hinge. Thus, a jammed hinge can be severed from the surface, allowing same to be driven by the remaining gear boxes, and the motor can be severed if a single motor is driving multiple gearboxes. None of the embodiments of the present invention use frangible elements.
U.S. Pat. No. 4,544,052 to Borden pertains to a coupling, rather than an actuator, that can be electrically disconnected, but must be manually reconnected. It entails the use of heavy compression springs to disconnect the load wherein these springs are released by electrically activating a small solenoid, allowing same to be disconnected quickly. Furthermore, this structure cannot be reconnected while the system is loaded or in motion. The design of the present invention permits both electrical connection and disconnection, both of which are achievable while the system is loaded and/or moving.
Continuing with U.S. Pat. No. 5,071,397 to Grimm, this design, similar to one of the embodiments of the present invention, also uses a hinge line planetary arrangement. However, the Grimm design has the disconnection occurring at the input shaft portion of the hinge line planetary. This feature does not allow the system to continue operating after a failure. The designs of the present invention use multiple actuators on a single surface. Thus, when one actuator fails (jammed or otherwise) it is removed from the system by disconnecting same and continuing operation with the remaining healthy actuator(s). If a jam occurred in the Grimm gear train, e.g., at the planet gear (item 2 in FIG. 1 thereof), while the input shaft would not be jammed, the output would be undesirably fixed in place. In the constructions of the present invention, the disconnection occurs at the point where the actuator couples to the load so that any jam anywhere in the actuator can be disconnected. In addition, in this Grimm device, the disconnecting mechanism is triggered automatically by an overload and will reset itself automatically when the overload is removed. The present invention uses electronics and software to continually monitor the system and evaluate same for unacceptable performance which may not necessarily manifest itself in an overload. When the decision is made to remove the actuator from the system, it is fully removed and cannot be re-engaged until commanded to (the system being stable in both the engaged and disengaged positions).
Turning now to U.S. Pat. No. 5,779,857 to Reilly, this design, similar to that of the present invention, disconnects at the actuator output. However, the Reilly disconnection is triggered by an overload of the input shaft. As already noted, an actuator failure may not always manifest itself as an overload and thus the Reilly design would not be tolerant of other types of failure. It should also be noted that even though the load is disconnected at the output, the overload sensing is at the input. Thus, if a failure occurred while the system was supposed to be dormant and holding a steady load, it would not disconnect if subjected to an excessive back driving load from the output. Only forward driving torque can activate the Reilly system. In addition, and differing from the structures of the present invention, it uses a frangible element to achieve the “jam-tolerant” mode. Frangible elements cannot be tested prior to use.
None of the noted prior art constructions utilize reversible disengagement without human intervention (testable on the vehicle) and the disengagement of the actuator from the load at or as close as is practicable to the output (closest to load). In addition, in the embodiments of the present invention, actuator fault (any type of failure or degradation is determined by monitoring, at a minimum, motor speed, motor load, and output load (with “motor” including any source of mechanical or hand power) and activating the electronically controlled disengagement mode.